Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $19.69   7.513%   $21.1693   $21.17   $21.15   $21.20  
  Purchase #2 $205.89   7.797%   $221.9432   $221.94   $221.95   $221.90  
  Purchase #3 $220.35   6.592%   $234.8755   $234.88   $234.90   $234.90  
  Purchase #4 $138.88   7.294%   $149.0099   $149.01   $149.00   $149.00  
  Purchase #5 $217.37   12.817%   $245.2303   $245.23   $245.25   $245.20  
  Purchase #6 $198.89   12.326%   $223.4052   $223.41   $223.40   $223.40  
  Purchase #7 $205.50   7.388%   $220.6823   $220.68   $220.70   $220.70  
  7 purchase totals = $1,206.57       $1,316.3157   $1,316.32   $1,316.35   $1,316.30